Add SELECT FOR UPDATE row lock on subscription before checking device
limit in all 3 device purchase endpoints (cabinet new, cabinet legacy,
miniapp). Without the lock, two concurrent requests both read the old
device_limit, both pass validation, and both increment — resulting in
device count exceeding max_device_limit (e.g., 5 devices when limit is 3).
Also moved max-devices check before balance check in legacy endpoint
to fail fast under lock.
Fringg
1cfede28b7